Vinculin directly binds zonula occludens-1 and is essential for stabilizing connexin-43-containing gap junctions in cardiac myocytes.

Vinculin (Vcl) links actin filaments to integrin- and cadherin-based cellular junctions. Zonula occludens-1 (ZO-1, also known as TJP1) binds connexin-43 (Cx43, also known as GJA1), cadherin and actin. Vcl and ZO-1 anchor the actin cytoskeleton to the sarcolemma. Given that loss of Vcl from cardiomyocytes causes maldistribution of Cx43 and predisposes cardiomyocyte-specific Vcl-knockout mice with preserved heart function to arrhythmia and sudden death, we hypothesized that Vcl and ZO-1 interact and that loss of this interaction destabilizes gap junctions. We found that Vcl, Cx43 and ZO-1 colocalized at the intercalated disc. Loss of cardiomyocyte Vcl caused parallel loss of ZO-1 from intercalated dics. Vcl co-immunoprecipitated Cx43 and ZO-1, and directly bound ZO-1 in yeast two-hybrid studies. Excision of the Vcl gene in neonatal mouse cardiomyocytes caused a reduction in the amount of Vcl mRNA transcript and protein expression leading to (1) decreased protein expression of Cx43, ZO-1, talin, and ß1D-integrin, (2) reduced PI3K activation, (3) increased activation of Akt, Erk1 and Erk2, and (4) cardiomyocyte necrosis. In summary, this is the first study showing a direct interaction between Vcl and ZO-1 and illustrates how Vcl plays a crucial role in stabilizing gap junctions and myocyte integrity.

Near-Peer Supervision in Primary Care: Bringing Teaching Teams From the Wards to the Clinic.

Background: Teaching near-peers yields numerous benefits to residents. Opportunities for near-peer teaching are typically restricted to hospital settings. Little is known about the educational potential of outpatient near-peer teaching. Objective: To describe Primary Care Teaching (PC Teach), a novel outpatient near-peer teaching experience for residents in a large, urban, internal medicine residency program; characterize its feasibility and acceptability; and evaluate changes in residents' self-reported confidence in outpatient teaching and attitudes toward teaching and primary care/outpatient medicine. Methods: In 2020-2021, following a didactic workshop, 43 postgraduate year 3 (PGY-3) residents at continuity clinics assigned to PC Teach completed a series of half-day sessions acting as preceptor to interns under attending supervision. Worksheets facilitated post-session feedback for residents and interns. Eighteen PGY-3s at nonparticipating clinics, who also completed the workshop, served as controls. We assessed process measures for feasibility and acceptability and analyzed resident attitudes using pre-post surveys. Results: Participating residents completed 2 to 8 sessions each. Post-intervention scores for confidence in outpatient teaching and attitudes toward teaching were greater, relative to pre-intervention group means, for intervention residents (median pre-post changes +0.60 [IQR 0.26, 1.26] and +0.46 [-0.04, 0.46], respectively) vs controls (-0.15 [-0.48, 0.85] and -0.36 [-0.86, 0.39]; between-group differences +0.75 [P=.03] and +0.82 [P=.02]). Changes in attitudes toward primary care/outpatient medicine did not differ significantly between intervention and control groups (+0.43 [-0.07, 0.68] and 0.04 [-0.58, 0.42]; between-group difference +0.39 [P=.12]). In multivariable analyses, odds of gains in confidence in outpatient teaching remained significantly larger for intervention residents vs controls. Conclusions: Implementing PC Teach with existing resources was feasible and acceptable, with program flexibility highlighted as a strength. Resident participation was associated with greater confidence in outpatient teaching.

Integrins protect cardiomyocytes from ischemia/reperfusion injury.

Ischemic damage is recognized to cause cardiomyocyte (CM) death and myocardial dysfunction, but the role of cell-matrix interactions and integrins in this process has not been extensively studied. Expression of α7ß1D integrin, the dominant integrin in normal adult CMs, increases during ischemia/reperfusion (I/R), while deficiency of ß1 integrins increases ischemic damage. We hypothesized that the forced overexpression of integrins on the CM would offer protection from I/R injury. Tg mice with CM-specific overexpression of integrin α7ß1D exposed to I/R had a substantial reduction in infarct size compared with that of α5ß1D-overexpressing mice and WT littermate controls. Using isolated CMs, we found that α7ß1D preserved mitochondrial membrane potential during hypoxia/reoxygenation (H/R) injury via inhibition of mitochondrial Ca2+ overload but did not alter H/R effects on oxidative stress. Therefore, we assessed Ca2+ handling proteins in the CM and found that ß1D integrin colocalized with ryanodine receptor 2 (RyR2) in CM T-tubules, complexed with RyR2 in human and rat heart, and specifically bound to RyR2 amino acids 165-175. Integrins stabilized the RyR2 interdomain interaction, and this stabilization required integrin receptor binding to its ECM ligand. These data suggest that α7ß1D integrin modifies Ca2+ regulatory pathways and offers a means to protect the myocardium from ischemic injury.